The proposed study has two major objectives: (1) to determine the ultrastructural changes which accompany failure to recover from acute episodes of total cerebral ischemia induced by hypovolemic hypotension; and (2) analysis of cerebral structures which might contribute to the generation or propagation of convulsive discharges in animals in which freeze lesions have been produced. Cortical electrical activity is monitored by means of the electrocorticogram in order to correlate structural lesions with the functional state of the tissue.